DOE OSTI2020
CaTi2O4 is Spinel-like structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are eight inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to four O2- atoms to form CaO4 tetrahedra that share corners with three CaO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 54–75°. There are a spread of Ca–O bond distances ranging from 2.19–2.24 Å. In the second Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with three CaO4 tetrahedra, corners with three TiO4 tetrahedra, and edges with six TiO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.25–2.31 Å. In the third Ca2+ site, Ca2+ is bonded to four O2- atoms to form CaO4 tetrahedra that share corners with three CaO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 57–71°. There are a spread of Ca–O bond distances ranging from 2.18–2.24 Å. In the fourth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent CaO4 tetrahedra, corners with four TiO4 tetrahedra, an edgeedge with one CaO6 octahedra, and edges with five TiO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.24–2.33 Å. In the fifth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six TiO4 tetrahedra, edges with two CaO6 octahedra, and edges with four equivalent TiO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.29–2.34 Å. In the sixth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six TiO4 tetrahedra, edges with two CaO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.29–2.40 Å. In the seventh Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share a cornercorner with one CaO4 tetrahedra, corners with five TiO4 tetrahedra, an edgeedge with one CaO6 octahedra, and edges with five TiO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.25–2.33 Å. In the eighth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six TiO4 tetrahedra, edges with two CaO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.30–2.41 Å. There are twelve inequivalent Ti3+ sites. In the first Ti3+ site, Ti3+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three CaO4 tetrahedra, corners with three TiO4 tetrahedra, edges with two equivalent CaO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 2.00–2.27 Å. In the second Ti3+ site, Ti3+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three equivalent CaO4 tetrahedra, corners with three equivalent TiO4 tetrahedra, edges with two CaO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 2.03–2.17 Å. In the third Ti3+ site, Ti3+ is bonded to four O2- atoms to form TiO4 tetrahedra that share corners with six CaO6 octahedra and corners with six TiO6 octahedra. The corner-sharing octahedra tilt angles range from 49–60°. There are a spread of Ti–O bond distances ranging from 1.86–1.94 Å. In the fourth Ti3+ site, Ti3+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent CaO4 tetrahedra, corners with four TiO4 tetrahedra, edges with three CaO6 octahedra, and edges with three TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.97–2.20 Å. In the fifth Ti3+ site, Ti3+ is bonded to four O2- atoms to form TiO4 tetrahedra that share corners with three CaO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 48–60°. There are a spread of Ti–O bond distances ranging from 1.89–1.95 Å. In the sixth Ti3+ site, Ti3+ is bonded to four O2- atoms to form TiO4 tetrahedra that share corners with six CaO6 octahedra and corners with six TiO6 octahedra. The corner-sharing octahedra tilt angles range from 51–60°. There are a spread of Ti–O bond distances ranging from 1.84–1.93 Å. In the seventh Ti3+ site, Ti3+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six TiO4 tetrahedra, edges with two equivalent TiO6 octahedra, and edges with four CaO6 octahedra. There are a spread of Ti–O bond distances ranging from 2.10–2.26 Å. In the eighth Ti3+ site, Ti3+ is bonded to four O2- atoms to form TiO4 tetrahedra that share corners with six CaO6 octahedra and corners with six TiO6 octahedra. The corner-sharing octahedra tilt angles range from 46–61°. There are a spread of Ti–O bond distances ranging from 1.87–1.98 Å. In the ninth Ti3+ site, Ti3+ is bonded to six O2- atoms to form TiO6 octahedra that share a cornercorner with one CaO4 tetrahedra, corners with five TiO4 tetrahedra, edges with three CaO6 octahedra, and edges with three TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 2.02–2.43 Å. In the tenth Ti3+ site, Ti3+ is bonded to four O2- atoms to form TiO4 tetrahedra that share corners with six CaO6 octahedra and corners with six TiO6 octahedra. The corner-sharing octahedra tilt angles range from 47–61°. There is two shorter (1.86 Å) and two longer (1.96 Å) Ti–O bond length. In the eleventh Ti3+ site, Ti3+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with three equivalent CaO4 tetrahedra, corners with three equivalent TiO4 tetrahedra, edges with two CaO6 octahedra, and edges with four TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 2.03–2.17 Å. In the twelfth Ti3+ site, Ti3+ is bonded to four O2- atoms to form TiO4 tetrahedra that share corners with three CaO6 octahedra and corners with nine TiO6 octahedra. The corner-sharing octahedra tilt angles range from 45–59°. There are a spread of Ti–O bond distances ranging from 1.88–1.95 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded to two Ca2+ and two Ti3+ atoms to form a mixture of distorted corner and edge-sharing OCa2Ti2 trigonal pyramids. In the second O2- site, O2- is bonded to two Ca2+ and two equivalent Ti3+ atoms to form distorted OCa2Ti2 trigonal pyramids that share a cornercorner with one OCaTi3 tetrahedra, corners with two equivalent OCa2Ti2 trigonal pyramids, and edges with three OCa2Ti2 trigonal pyramids. In the third O2- site, O2- is bonded to one Ca2+ and three Ti3+ atoms to form a mixture of distorted corner and edge-sharing OCaTi3 trigonal pyramids. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Ti3+ atoms. In the fifth O2- site, O2- is bonded to two Ca2+ and two Ti3+ atoms to form distorted OCa2Ti2 trigonal pyramids that share a cornercorner with one OCaTi3 tetrahedra, corners with two OCa2Ti2 trigonal pyramids, an edgeedge with one OCaTi3 tetrahedra, and an edgeedge with one OCa2Ti2 trigonal pyramid. In the sixth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the eighth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the ninth O2- site, O2- is bonded to one Ca2+ and three Ti3+ atoms to form a mixture of distorted corner and edge-sharing OCaTi3 tetrahedra. In the tenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Ca2+ and two Ti3+ atoms. In the eleventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the twelfth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Ca2+ and two Ti3+ atoms. In the thirteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the fourteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the fifteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the sixteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the seventeenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Ca2+ and two Ti3+ atoms. In the eighteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two Ca2+ and two Ti3+ atoms. In the nineteenth O2- site, O2- is bonded to two Ca2+ and two equivalent Ti3+ atoms to form corner-sharing OCa2Ti2 tetrahedra. In the twentieth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the twenty-first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the twenty-second O2- site, O2- is bonded in a 4-coordinate geometry to four Ti3+ atoms. In the twenty-third O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms. In the twenty-fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ti3+ atoms.